The present invention relates to a method and apparatus for performing sensory nerve conduction studies.
Sensory nerve conduction studies are often used by neurologists to diagnose different forms of nerve compression syndrome. Diminished conduction velocity may indicate nerve damage. Such studies may also be used to indicate the development or onset of an abnormal condition. Such studies could, therefore, be used to permit corrective action to be undertaken before permanent damage to the nerve occurs.
In one example, nerve conduction studies could be used to diagnose or determine the potential for or the onset of carpal tunnel syndrome. Carpal tunnel syndrome is a painful condition associated with repetitive use of the hands and wrists. The condition is caused by compression of the median nerve as it passes through the carpal tunnel. Carpal tunnel syndrome is characterized by pain and paresthesia in the sensory distribution of the median nerve in the hand. Symptoms include numbness, tingling and a painful burning sensation in the fingers which can radiate up the forearm to the shoulder.
Heretofore, nerve conduction velocity measurements have been made by stimulating the peripheral nerve with an electrical impulse and measuring the time or latency from the stimulation until an action potential occurs in a muscle innervated by the nerve under examination. Measurements are made by the use of surface electrodes positioned over the muscle that picks up the signals which are then amplified and displayed on a screen of a cathode ray tube or an oscilloscope. Measurements of the distance between the stimulus and response, which peak on the screen of the oscilloscope, are converted into latency times. This technique is referred to as electromyography (EMG). U.S. Pat. No. 4,291,705 entitled NEUROMUSCULAR BLOCK MONITOR, which issued on Sep. 29, 1981 to Severinghaus et al, and U.S. Pat. No. 4,807,643 entitled DIGITAL ELECTRONEUROMETER, which issued on Feb. 28, 1989 to Rosier, disclose methods and apparatus for performing conduction studies, the disclosure of which are hereby incorporated by reference.
EMG generally requires sophisticated and expensive equipment. The studies are typically performed by highly trained medical personnel or technicians. Proper procedures must be followed or error will be present in the results. For example, in conducting a median nerve sensory fiber conduction study, the distance between the stimulating cathode and the recording electrode is critical to obtaining results which may be compared with generally accepted standards or norms. Another source of error involves ambient temperature. Lower temperature will reduce the conduction velocities. In addition, it is important that the electrodes be placed properly on the subject so that the appropriate nerve and responses to stimulation are accurately recorded.
A need exists for apparatus which eliminates measurement errors and assists in the proper placement of electrodes for nerve conduction studies. In addition, a need exists for apparatus which permits nonmedical personnel to conduct studies on a regular basis at reduced cost and with accurate results.